1. Field of the Invention
The field of the invention generally relates to propeller blades for aircraft and in particular, propeller blades for aircraft having means to prevent the buildup of ice thereon.
2. Description of Related Art
Propellers fitted to aircraft that are approved for flight into known icing conditions must include provisions to prevent unacceptable levels of ice accumulation on the propeller blades. Ice build-up on the aerofoil sections of a propeller blade affects the aerodynamic efficiency of the blade. It is therefore desirable to limit the amount of ice that is allowed to accumulate on the blades, to reduce the loss of aerodynamic efficiency. In addition, to prevent damage to the aircraft fuselage in icing conditions, it is desirable to minimize the size of lumps of ice that are shed from the propellers.
In the prior art, an electrical heater system is controlled by a timer to provide cyclic heating of the blades to control the shedding of ice. The heater system includes an electrical heater blanket on each blade, cabling to connect the heater system to the electrical supply, a means to allow the electrical supply to be transferred from the airframe to the rotating propeller, for instance slip-rings and carbon brushes, and an electronic deicing timer. In use, the heater is a considerable drain on the aircraft electrical generator system. Additionally, in the event that the blades are heated excessively, the melted ice can runback and reform behind the electrically deiced area. This is a potentially hazardous condition for an aircraft. Such electrical heating systems typically require in excess of 1200 watts of electrical power per blade to remove ice effectively. The electrical heating blankets extend all the way to the propeller centrebody which provides the aerodynamic interface to the aircraft nacelle. A further drawback of the prior art heating systems is that damage to a heater element can prevent the entire element from functioning.